INTRODUCTION — The evaluation and management of human bite wounds will be discussed here.
Issues related to animal bite wounds are discussed separately. (See "Animal bites (dogs, cats, and other animals): Evaluation and management".)
EPIDEMIOLOGY — It is estimated that 250,000 human bites occur each year in the United States; up to 25 percent of these injuries become infected [1,2]. The likelihood of infection after a human bite is determined by the depth and location of the wound and host factors; the infection rate ranges from 2 percent for superficial wounds, less than 10 percent for occlusal bites, to over 25 percent for clenched-fist wounds or other wounds on the hand [2-4].
MICROBIOLOGY — Relevant pathogens in the setting of human bite wounds include human oral flora (Eikenella, group A Streptococcus, Fusobacterium, Peptostreptococcus, Prevotella, and Porphyromonas spp) and human skin flora (such as staphylococci and streptococci) [5-7]. In addition, human bite wounds may be associated with transmission of viral pathogens including hepatitis B, hepatitis C, HIV, and herpes simplex virus [8-13].
In one study including 50 patients with infected human bites, the median number of isolates per wound culture was four; aerobes and anaerobes were isolated from 54 percent of wounds, aerobes alone were isolated from 44 percent, and anaerobes alone were isolated from 2 percent [7]. Eikenella corrodens are fastidious organisms and are often misidentified.
CLINICAL EVALUATION
History and physical examination — Human bite wounds can occur as a result of incidental or purposeful injury [14,15].
Incidental injury may include "love nips" (to the face, breasts, or genital areas) or self-inflicted wounds (such as paronychia due to nail biting or thumb-sucking) [16,17]. (See "Paronychia".)
Purposeful injury may result in occlusal bites or clenched-fist injuries with the following findings [18]:
●Occlusal bites – Occlusal bites are frank bites by human teeth, most often to the fingers, hands, or arms. In adolescents and adults, occlusal bites to the breasts or genitalia during sexual activity or assault may occur. Bites appear as a semicircular or oval area of erythema or bruising. The skin may or may not be intact; bites with intact skin are not generally associated with infection. Occlusal bites occur most commonly in young children and adult women.
In children, occlusal bites typically occur on the face, upper extremities, or trunk as the result of aggressive play; such wounds are often trivial [19]. However, a bite mark on a child with maxillary intercanine distance (distance between left and right canine from the outer edge of the tooth) >2.5 cm suggests the bite came from an adult and should raise concern for child abuse (picture 1) [20]. (See "Physical child abuse: Recognition", section on 'Inflicted bruises'.)
●Clenched-fist injuries – Clenched-fist injuries are traumatic lacerations that occur when the clenched-fist of one person strikes the teeth of another (figure 1). They occur most commonly in adolescent boys and adult men [21,22]. Skin breaks over the knuckles can lead to the introduction of both skin and oral flora into fascial layers of the hand, with potential spread to the nearby joint and soft tissues [21,22]. The lacerations are small (usually ≤15 mm) and typically occur over the third and fourth metacarpophalangeal or proximal interphalangeal joints of the dominant hand.
Many patients ignore these wounds until the onset of pain, swelling, or purulent discharge; as a result, these injuries are often complicated by established infection at the time patients seek medical attention. For these reasons, wounds over or near the metacarpophalangeal joints should be explored carefully in the anatomic and the clenched-fist position to assess for damage to the underlying tendon sheath, fascia, joint capsule, and metacarpal head.
Human bite wounds should be evaluated carefully for a tooth or other foreign material, signs of infection, and neurovascular status distal to the wound. Hand wounds should be examined with fingers extended and in the clenched-fist position. In a case series of including 50 patients with infected human bites, the median time from the bite to the first signs of infection was approximately 24 hours; signs as early as two hours after the bite occurred in some cases [7].
Bite wound infection may be superficial (eg, cellulitis, with or without abscess) or deep (abscess, septic arthritis, osteomyelitis, tenosynovitis, or necrotizing soft tissue infection):
●Signs of superficial infection – Clinical manifestations of cellulitis include fever, tenderness, erythema, swelling, and warmth; purulent drainage and/or lymphangitis may be present. An associated superficial abscess may present as a tender, erythematous, fluctuant nodule.
●Signs of deep infection – In addition to the above manifestations, clues for deep infection include persistent or progressive pain several days following the initial injury, pain with passive movement, pain out of proportion to exam findings, crepitus, joint swelling, systemic illness (fever, hemodynamic instability), and persistent signs of infection despite initial wound care and antibiotic administration.
The level of suspicion for deep infection should be increased for patients with immunosuppression (including diabetes) or neuropathy; these patients often present later in their course with increased risk of serious infection and limited pain on clinical exam.
Clinical manifestations of wound infection and associated complications are described further separately. (See "Cellulitis and skin abscess: Epidemiology, microbiology, clinical manifestations, and diagnosis" and "Septic arthritis in adults" and "Nonvertebral osteomyelitis in adults: Clinical manifestations and diagnosis" and "Infectious tenosynovitis" and "Necrotizing soft tissue infections".)
Laboratory testing — For patients with clinically uninfected bite wounds, laboratory studies are not indicated. Similarly, wound cultures are not indicated; such results do not correlate with subsequent infection.
For patients with clinically infected bite wounds, laboratory studies (eg, complete blood count and serum inflammatory markers such as erythrocyte sedimentation rate, C-reactive protein) are reasonable if there is clinical concern for osteomyelitis. In addition, wound cultures (aerobic and anaerobic) should be obtained from infected bite wounds to establish the microbiology of the infection and to guide antibiotic therapy. The laboratory requisition should note that a human bite wound is the culture source; E. corrodens is a common isolate and a fastidious organism that may be misidentified if proper culture techniques are not used.
Bacteremia may occur in the setting of superficial or deep infection. Blood cultures should be obtained in patients with fever or other signs of systemic infection and patients who are immunosuppressed. In other patients, the yield of blood cultures is typically low and the risk of false positives likely outweighs the benefit.
Issues related to testing (baseline and follow-up) for prevention of HIV, hepatitis B, and hepatitis C are discussed separately. (See "Management of nonoccupational exposures to HIV and hepatitis B and C in adults".)
Imaging — Patients with clenched-fist injuries warrant plain radiographs to evaluate for evidence of fracture or joint disruption or retained foreign body. Further imaging of these wounds is usually not obtained because these patients warrant timely surgical exploration, debridement, and irrigation regardless of additional findings on imaging.
In patients with other types of bites that appear to be clinically uninfected, plain radiographs are typically unnecessary but may be obtained if the bite is deep and bone/joint disruption and/or presence of a foreign body is suspected. For patients with infected bites, ultrasound may help distinguish cellulitis from a drainable abscess. (See "Techniques for skin abscess drainage", section on 'Bedside ultrasonography'.)
MANAGEMENT — Patients may seek care for evaluation of bite injury (in absence of infection) or established bite infection.
Uninfected bite — For patients with a human bite injury in the absence of clinical evidence for infection (on physical examination or imaging), components of management include wound care and foreign body removal (if present). In addition, the need for antibiotic prophylaxis as well as interventions for prevention of tetanus, hepatitis B, and HIV should be assessed.
Wound management
Local wound care — Appropriate local wound care is the most important factor for preventing infection in patients with bite wounds [14]. Components include (see "Basic principles of wound management"):
●Control of bleeding (direct pressure should be applied to actively bleeding wounds).
●Clean the wound with soap and water, povidone iodine, or other antiseptic solution.
●Provide local anesthesia, followed by irrigation with sterile saline and removal of grossly visible debris. Clinically uninfected bite wounds should not be cultured; results are not predictive of subsequent infection [23]. (See "Subcutaneous infiltration of local anesthetics" and "Clinical use of topical anesthetics in children" and "Minor wound evaluation and preparation for closure".)
●Carefully re-examine the clean wound. (See 'History and physical examination' above.)
●Determine whether wound closure is appropriate. (See 'Closure' below.)
Surgical consultation — Surgical consultation is warranted in the following circumstances [24]:
●Clenched-fist wounds
●Complex facial lacerations (see "Assessment and management of facial lacerations")
●Deep wounds, especially if significant avulsion or amputation is present
●Wounds associated with neurovascular compromise
Closure — In general, human bite wounds should not be closed primarily, given high risk for the development of infection. Such wounds should be irrigated copiously, dressed, and evaluated daily for signs of infection.
Facial laceration may be a reasonable exception, given the cosmetic importance of this area [14,23,24]. Such wounds may be closed primarily if they are clinically uninfected and ≤24 hours old [23]. Subcutaneous sutures should be used sparingly; foreign material in a contaminated wound increases the risk of infection [23]. Bite wounds should not be closed with tissue adhesive ("glue").
Patients who undergo primary closure warrant antibiotic prophylaxis. (See 'Antibiotic prophylaxis' below.)
Antibiotic prophylaxis
Indications — The likelihood of infection after a human bite is determined by the depth and location of the wound and host factors; it ranges from 2 percent for superficial wounds to over 25 percent for clenched-fist wounds or other wounds on the hand [2-4]. In one randomized study including 48 patients with human bites to the hand; infection developed in 46 percent of patients who did not receive antibiotic prophylaxis; no infection developed among the patients who did receive antibiotic prophylaxis [3].
Trivial human bites that do not break the skin or are very superficial do not require prophylaxis [4].
We suggest antibiotic prophylaxis for patients with clinically uninfected wounds and any one of the following features which further increase the risk of infection [5,25]:
●Lacerations undergoing primary closure and wounds requiring surgical repair
●Wounds on the hand(s), face, or genital area
●Wounds in close proximity to a bone or joint (including prosthetic joints)
●Wounds in areas of underlying venous and/or lymphatic compromise (including vascular grafts)
●Wounds in immunocompromised hosts (including diabetes)
●Wounds with associated crush injury
In the absence of the above factors, we do not favor use of antibiotic prophylaxis. However, some experts do favor routine use of antibiotic prophylaxis for human bites, even in the absence of the above factors.
Antibiotic administration — Antibiotic prophylaxis should include empiric coverage of human oral and skin flora; appropriate agents are outlined in the table (table 1). These regimens also include reasonable coverage of methicillin-susceptible Staphylococcus aureus and streptococci. (See 'Microbiology' above.)
The preferred antibiotic agent for prevention of infection due to human bite wounds is amoxicillin-clavulanate (table 1) [5].
Agents lacking activity against E. corrodens should be avoided; these include first-generation cephalosporins (such as cephalexin), penicillinase-resistant penicillins (such as dicloxacillin), macrolides (such as erythromycin), clindamycin, and aminoglycosides. However, clindamycin may be used for anaerobic coverage if it is administered in conjunction with an additional agent that is active against E. corrodens.
The duration of prophylactic oral antibiotics is three to five days, with close follow-up [5]. Signs of infection on follow-up examination should prompt further evaluation and empiric antibiotic therapy.(See 'Infected bite' below and 'Antibiotic therapy' below.)
Infected bite — For patients with a human bite and clinical evidence for infection (on physical examination and/or imaging), components of management include assessing the need for surgical consultation, debridement, foreign body removal (if present), sending cultures (wound cultures as well as blood cultures), and administration of antibiotic therapy [23]. In addition, the need for interventions for prevention of tetanus, rabies, hepatitis B, and HIV should be assessed.
Surgical consultation — Surgical consultation for bite-associated infection is warranted in the following circumstances [24]:
●Deep infection (abscess, septic arthritis, osteomyelitis, tenosynovitis, or necrotizing soft tissue infection)
●Clenched-fist wounds and other hand wounds
●Infections involving the face
●Infection associated with neurovascular compromise
●Infection with associated foreign body requiring removal
●Infection in immunocompromised hosts (including diabetes) or patients with venous stasis
●Rapidly progressive infection
●Persistent signs and symptoms of infection despite appropriate antibiotic therapy
Specimens obtained at the time of debridement should be sent for Gram stain, aerobic, and anaerobic bacterial cultures to identify the causative pathogen(s), prior to initiation of antibiotics. The laboratory requisition should note that a human bite wound is the culture source.
In general, infected bite wounds should be left open following debridement, with approximation of wound edges to facilitate closure by secondary intention.
Debridement — Debridement of infected tissue is an important component of management for infection associated with a human bite. If previously repaired, suture material should be removed. Associated abscess(es) should be drained. (See "Techniques for skin abscess drainage".)
Antibiotic therapy — Antibiotic therapy should be administered to patients with suspected or known bite-associated infection, following collection of blood cultures and wound cultures.
Spectrum of therapy — Antibiotic therapy should include empiric coverage of human oral and skin flora; appropriate agents are outlined in the tables (table 1 and table 2). These regimens include reasonable coverage of methicillin-susceptible S. aureus and streptococci. (See 'Microbiology' above and 'Antibiotic prophylaxis' above.)
For patients with risk factors for colonization with methicillin-resistant S. aureus (MRSA) (table 3), empiric antibiotic coverage for MRSA may be important. Issues related to risk factors and treatment of MRSA are discussed further separately. (See "Methicillin-resistant Staphylococcus aureus (MRSA) in adults: Treatment of skin and soft tissue infections" and "Methicillin-resistant Staphylococcus aureus (MRSA) in adults: Epidemiology".)
Route and duration of therapy — Patients with mild infection may be treated with oral antibiotics (table 1).
Treatment with parenteral antibiotics (table 2) is warranted in the following circumstances:
●Systemic signs of toxicity (eg, fever >100.5°F/38°C, hypotension, or sustained tachycardia)
●Deep infection (septic arthritis, osteomyelitis, tenosynovitis, bacteremia, or necrotizing soft tissue infection)
●Rapid progression of erythema
●Progression of clinical findings after 48 hours of oral antibiotic therapy
●Inability to tolerate oral therapy
●Proximity of the lesion to an indwelling device (eg, prosthetic joint or vascular graft)
The decision to initiate parenteral therapy should be based on individual clinical circumstances, such as severity of clinical presentation and patient comorbidities. As an example, the presence of an immunocompromising condition should lower the threshold for parenteral therapy.
Patients with superficial wound infection (in the absence of abscess) may be managed with wound debridement and oral antibiotic therapy (table 1) to complete a course of 5 to 14 days, with close outpatient follow-up. Antibiotic therapy should be continued at least one to two days after signs and symptoms have resolved; this is typically less than seven days, but longer treatment may be needed if there is slow resolution of skin and soft tissue findings.
Patients with superficial abscess (in the absence of bacteremia) who undergo drainage may be managed with initial parenteral antibiotic therapy until infection is resolving, followed by oral therapy to complete a course of 5 to 14 days, with close outpatient follow-up; as mentioned above, a longer course of treatment is used in patients who have a slow response to treatment [5].
Antibiotic therapy should be tailored to culture and susceptibility data when available.
In the setting of bacteremia, the approach to antibiotic therapy depends on the nature of the pathogen identified (see related topics). Patients with complicated infections (such as tenosynovitis, septic arthritis, or osteomyelitis) require prolonged therapy tailored to individual circumstances [5]; consultation with infectious disease expertise is warranted in such cases. (See "Infectious tenosynovitis" and "Septic arthritis in adults" and "Nonvertebral osteomyelitis in adults: Treatment".)
In patients with infection not requiring debridement or drainage, decisions regarding likely pathogens should be made based on the clinical history and patient risk factors. (See 'Microbiology' above.)
OTHER PREVENTIVE INTERVENTIONS
Tetanus prophylaxis — Human bites are considered tetanus-prone wounds. Tetanus prophylaxis is warranted for patients with bites that break the skin, as indicated (table 4). (See "Tetanus-diphtheria toxoid vaccination in adults".)
Preventing HIV, HBV, and HCV — In general, the risk of contracting HIV, hepatitis B, or hepatitis C from a human bite is negligible unless blood exposure has also occurred. If the biter has been exposed to blood from an infected bite victim, then prophylaxis may be appropriate as discussed separately. (See "Management of nonoccupational exposures to HIV and hepatitis B and C in adults".)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Skin and soft tissue infections" and "Society guideline links: Human bites".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Beyond the Basics topic (see "Patient education: Animal and human bites (Beyond the Basics)")
SUMMARY AND RECOMMENDATIONS
●Purposeful human bites may result in occlusal bites or clenched-fist injuries (see 'History and physical examination' above):
•Occlusal bites occur most frequently on the fingers, hands, or arms; they present as a semicircular or oval area of erythema or bruising. The skin may or may not be intact.
A bite mark on a child with maxillary intercanine distance (distance between left and right canine from the outer edge of the tooth) >2.5 cm suggests the bite came from an adult and should raise concern for child abuse (picture 1). (See "Physical child abuse: Recognition", section on 'Inflicted bruises'.)
•Clenched-fist injuries occur when the clenched-fist of one person strikes the teeth of another (figure 1); lacerations are typically over the third and fourth metacarpophalangeal or proximal interphalangeal joints of the dominant hand.
Clenched-fist injuries are highly prone to superficial and/or deep infection, given the proximity of the skin over the knuckles to the joint capsule. Many patients ignore these wounds until pain, swelling, or purulent discharge develops; as a result, such injuries are often complicated by established infection at the time patients seek medical attention.
●Human bite wounds should be evaluated carefully for foreign material, signs of infection, and neurovascular status distal to the wound. Hand wounds should be examined with both the fingers extended and clenched into a fist. (See 'History and physical examination' above.)
●Bite wound infection may be superficial (eg, cellulitis, with or without abscess) or deep (abscess, septic arthritis, osteomyelitis, tenosynovitis, or necrotizing soft tissue infection). (See 'History and physical examination' above.)
•Clinical manifestations of superficial infection include fever, erythema, swelling and/or warmth, purulent drainage, and/or lymphangitis. An associated superficial abscess may present as a tender, erythematous, fluctuant nodule.
•In addition to the above manifestations, clues for deep infection include persistent or progressive pain several days following the initial injury, pain with passive movement, pain out of proportion to exam findings, crepitus, joint swelling, systemic illness (fever, hemodynamic instability), and persistent signs of infection despite initial wound care and antibiotic administration.
●Patients with clenched-fist injuries warrant plain radiographs to evaluate for evidence of bone or joint disruption or retained foreign body. In patients with other types of bites that appear to be clinically uninfected, plain radiographs are typically unnecessary but may be obtained if the bite is deep and bone/joint disruption and/or presence of a foreign body is suspected. For patients with infected bites, ultrasound may help distinguish cellulitis from a drainable abscess. (See 'Imaging' above and "Techniques for skin abscess drainage", section on 'Bedside ultrasonography'.)
●For patients with a human bite injury in the absence of clinical evidence for infection (on physical examination or imaging), components of management include local wound care and foreign body removal (if present). In addition, tetanus prophylaxis should be provided, as needed (table 4). (See 'Uninfected bite' above.)
•Surgical consultation is warranted for patients with clenched-fist wounds, complex facial lacerations, deep wounds (especially if significant avulsion or amputation is present), and wounds with neurovascular compromise.
•We suggest that most human bite wounds be left open to heal by secondary intention (rather than closed primarily), given the high risk for the development of infection (Grade 2C). Such wounds should be irrigated copiously, dressed, and evaluated daily for signs of infection. Closure of clinically uninfected facial lacerations may be a reasonable exception to this approach, given the cosmetic importance of this area. In addition, tetanus vaccination should be provided, as needed (table 4). (See 'Closure' above.)
•We suggest administering antibiotic prophylaxis for patients with clinically uninfected wounds in the following circumstances (Grade 2C) (see 'Antibiotic prophylaxis' above):
-Lacerations undergoing primary closure and wounds requiring surgical repair
-Wounds on the hand(s), face, or genital area
-Wounds in close proximity to a bone or joint (including prosthetic joints)
-Wounds in areas of underlying venous and/or lymphatic compromise (including vascular grafts)
-Wounds in immunocompromised hosts (including diabetes)
-Wounds with associated crush injury
●For patients with a human bite and clinical evidence for infection (on physical examination and/or imaging), components of management include debridement, foreign body removal (if present), obtaining wound and blood cultures, administration of antibiotic therapy, and, as needed, tetanus prophylaxis. In addition, surgical consultation is indicated for infected clenched-fist and other hand wounds, facial infections, deep infections (eg, tenosynovitis, septic arthritis, or osteomyelitis), or complicated wounds. (See 'Infected bite' above and 'Surgical consultation' above.)
●Antibiotic regimens (for antibiotic prophylaxis or antibiotic therapy) should include empiric coverage of human oral and skin flora. Amoxicillin-clavulanate is the preferred oral agent; dosing and alternative regimens are summarized in the tables (table 1 and table 2). Administration of parenteral antibiotics is warranted in the following circumstances (see 'Microbiology' above and 'Antibiotic prophylaxis' above and 'Antibiotic therapy' above):
•Systemic signs of toxicity (eg, fever >100.5°F/38°C, hypotension, or sustained tachycardia)
•Deep infection (septic arthritis, osteomyelitis, tenosynovitis, bacteremia, or necrotizing soft tissue infection)
•Rapid progression of erythema
•Progression of clinical findings after 48 hours of oral antibiotic therapy
•Inability to tolerate oral therapy
•Proximity of the lesion to an indwelling device (eg, prosthetic joint or vascular graft)
●In general, the risk of contracting HIV, hepatitis B, or hepatitis C from a human bite is negligible, unless blood exposure has also occurred. If the biter has been exposed to blood from an infected bite victim, then prophylaxis may be appropriate as discussed separately. (See "Management of nonoccupational exposures to HIV and hepatitis B and C in adults".)
